Intensive research is presently underway to obtain fusion energy from the nuclear reactions of light elements, such as isotopes of hydrogen or helium, in a controlled manner so that this energy may be used for generating electric power. The nuclear reactors now in use for generating electric power operate by fission in which heavy nuclei are broken up into fission-fragment nuclei, whereas fusion reactors would operate by fusion of light nuclei in which energy-rich light nuclei are fused together to form heavier and less energy-rich fusion products.
A fusion reactor has some distinct advantages over a fission reactor. Whereas the fission process yields radioactive end products of high biological hazard and long life, the ashes of fusion would be non-radioactive nuclei, and there would be no problem of disposal of radioactive waste products. The fuel for a fusion reactor is in unlimited abundance. Isotopes of hydrogen such as deuterium may be obtained from water. And finally, controlled nuclear fusion reactors are safe to operate because only a small amount of fuel is contained within the reactor at a given time, thereby eliminating the possibility of an explosive, or runaway reaction.
To achieve controlled fusion it is necessary to heat a gas to extremely high temperature to form a plasma to initiate the reaction, and then contain the plasma without appreciable loss for a sufficiently long time to yield a net power output. The containment of this hot plasma, having a temperature in excess of 100 million degrees Kelvin, is a formidable undertaking. No material is available for constructing a container that would not be melted by this hot plasma.
Plasma is composed of an equal mixture of positively charged nuclei and free electrons. To maintain the plasma purity it can't be allowed to contact any other matter. Thus, it must be contained in a hermetically sealed vacuum chamber, and the fusible nuclei must not be allowed to touch the chamber walls before they have had sufficient opportunity to collide and fuse. However, at fusion temperature the nuclei are moving so rapidly they would travel from wall to wall of any chamber of practical size in less than a millionth of a second.
Thus, a nonmaterial means must be found to contain the plasma from contact with the chamber walls long enough for a net release of fusion power. One approach is to employ a magnetic field to confine the hot plasma. A circular ring of plasma is generated and maintained within a toroid or a doughnut shaped region by the action of intense magnetic fields shaped to form the toroid. The magnetic field acts as a nonmaterial container liner that insulates the hot plasma from the container walls. The magnetic field exerts an effective pressure on the contained plasma that is proportional to the square of the magnetic field strength. By maintaining this magnetic pressure at a greater value than the internal pressure of the plasma, containment is possible.
It may therefore be understood that it is necessary to develop a means for generating a high density magnetic field that is shaped to form a toroid insulating liner within a structural toroid, the magnetic field being of sufficient intensity to contain the hot plasma therein.